Camshaft adjuster for internal combustion engines

ABSTRACT

A camshaft adjuster ( 1 ) for internal combustion engines has a central tensioning screw ( 9 ) for fixing the adjuster ( 1 ) in relation to a camshaft ( 2 ). A slide ( 8 ) controls the supply of the pressure medium to the camshaft adjuster ( 1 ) being integrated into the tensioning screw ( 9 ). The tensioning screw ( 9 ) forms the mounting of the camshaft adjuster ( 1 ) in relation to the camshaft ( 2 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national phase filing of PCT/EP99/02495 filedApr. 14, 1999, which claims priority to German Patent Application 198 17319.9 filed Apr. 18, 1998, which applications are herein expresslyincorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a camshaft adjuster for internal combustionengines.

Camshaft adjusters are known in the form of piston-type adjusters withan axially displaceable piston (DE 40 29 849 C2, DE 196 11 365 A1 and DE197 26 300 A1) and in the form of vane-type adjusters with vanes thatcan be acted upon and pivoted in the circumferential direction. Inconnection with both designs, the camshaft adjuster is fixed as anend-mounted extension of the camshaft by means of a central clampingscrew.

For the purpose of controlling the hydraulic pressure supply to thecamshaft adjuster, DE 40 29 849 C2 discloses the provision of anexternal 4/2-way valve, from which supply passages run to the camshaftand to the actuating piston that is provided here as the actuating meansand is arranged in an accommodation space between the inner element andthe outer element, the drive connection to the crankshaft running viathe outer element.

The long conduit paths that this entails, with the risk of correspondingleaks and of a certain elasticity, can have the effect that the systemhas inadequate hydraulic rigidity and thus makes satisfactory controlmore difficult, not to mention the fact that the external arrangement ofthe control device formed by the directional control valve has anegative effect in terms of the outlay on construction and the size ofthe installation space required.

DE 196 11 365 A1 discloses integration of the control device designed asa multi-way valve into the clamping screw. The result is that the latteracts as a housing to form an axial receptacle for a centrally situatedand axially displaceable control spool via which pressure medium can besupplied to the actuating means radially along short paths.

In view of this, provision is made to guide the camshaft adjuster'sinner element, which is fixed in terms of rotation relative to thecamshaft, the camshaft adjuster's outer element, which can be turnedrelative to the inner element and via which the drive connection to thecrankshaft runs, on the clamping screw, irrespective of centering of theinner element relative to the camshaft independently of this. Thisrequires very narrow tolerances, that is to say a high outlay onmanufacture, and furthermore leads to misalignment errors due to thecumulative effect of a number of radial guides subject to play, theseerrors potentially having disadvantageous effects on concentricity ofrunning and vibration, such concentricity and misalignment errors alsomake it more difficult to operate the control spool by means of theaxially offset actuating magnet as actuator, associated with the spoolon the housing side, with the minimum clearance relative to the armaturecarried by the control spool. However, larger clearances lead to a needfor more power and hence for more space, and, given the conditions ofconstruction in the case of internal combustion engines for motorvehicles, this is often not available, if only because of the axialextension entailed by the camshaft adjuster.

SUMMARY OF THE INVENTION

The object of the present invention is to construct a camshaft adjusterof the type stated at the outset in such a way that optimum centering ofthe camshaft adjuster is achieved. This centering simultaneously createsthe conditions for particularly simple and economical manufacture.

According to the invention, this is achieved by the clamping screwforming the element of the camshaft adjuster that effects centeringrelative to the camshaft, eliminating the need to provide the adjusterwith any further centering support as regards its inner and outerelement and its lateral closure elements in the form of covers. Thiseliminates the need for axial undercuts or projections on the inner andouter elements, which would make manufacture more difficult. Moreover,the configuration according to the invention, involving centering of theentire camshaft adjuster, including the connection of the control deviceformed by the multi-way valve to the actuator, by means of the clampingscrew, creates particularly favorable conditions for largelytolerance-free centering without excessive demands as to manufacture,with ideal conditions for optimum, vibration-free concentricity ofrunning and with the minimum required clearances at the transitionbetween the control spool and the actuator.

As a refinement of the invention, the inner element and the outerelement can be designed with flat end faces, that is to say formdisc-shaped elements, which are covered over a certain area by annularcovers, with the result that the covers require only axial clamping. Ithas proven expedient here if the covers adjoin the centering collar ofthe camshaft radially on the inside, providing sufficient radial overlapwith the inner and outer elements to allow the use of simple sealingmeans in so far as these are to be used, the precise centering withsmall clearances achieved by means of the invention also having anadvantageous effect as regards the reduction of leakage.

The refinement according to the invention of using disc-shaped inner andouter elements and covers leads to particularly far-reachingsimplifications in the case of camshaft adjusters designed as vane-typeadjusters.

From the following detailed description, taken in conjunction with thedrawings and subjoined claims, other objects and advantages of thepresent invention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and features of the invention will become apparent fromthe claims. The invention will furthermore be explained with additionaldetails by means of the drawings in which:

FIG. 1 is a partially schematic longitudinal section view through acamshaft adjuster according to the invention, along the line I—I in FIG.2;

FIG. 2 is a section view along line II—II in FIG. 1; and

FIG. 3 is a view substantially similar enlarged representation of thecentral area of the camshaft adjuster shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The camshaft adjuster shown in FIGS. 1 to 3 is denoted overall by thenumeral 1 and is shown in association with a camshaft 2 of an internalcombustion engine 3, which is shown here only in outline and on the endof which that is associated with the illustrated end of the camshaft 2 achain case 4 (shown essentially only in outline) is provided. Providedon this chain case 4, as an axial extension of the camshaft 2 andsituated opposite the latter, is the actuator 5 associated with thecamshaft adjuster 1. The actuator is formed by an actuating magnet andis bolted onto the outside of that end of the chain case 4 which isremote from the internal combustion engine 3, as indicated at 6.

The actuator 5 formed by an actuating magnet interacts with the armature7 of a control spool 8, which is integrated into a central screw in theform of a clamping screw 9, by means of which the camshaft adjuster 1 isflanged onto the end of the camshaft 2, the clamping screw 9, thecontrol spool 8 of the camshaft adjuster 1 and the actuator 5 beingcoaxial with the camshaft 2.

Seated on the clamping screw 9 and clamped axially against the camshaft2 is the inner element 110 of the camshaft adjuster 1 and associatedwith it is an outer element 111, which has teeth 12 on its outercircumference, by means of which the camshaft 2 is driven by thecrankshaft (not shown here) of the internal combustion engine 3 in afixed relationship with respect to direction and speed of rotation. Thechain drive discussed and indicated here could, of course, also bereplaced by other types of drive connection, such as toothed-belt drivesor gear mechanisms.

Distributed over its circumference, the outer element 111 has pistonvanes 13, associated with which on the inner element 110 are matingvanes 14, respective pairs of mating vanes 14 delimiting a ring sector15 in which a piston vane 13 of the outer element 111 is located, theouter element 111 forming, with the piston vanes 13 associated with it,as it were a vaned rotor which can be adjusted relative to the innerelement 110 over an angular range limited by the mating vanes 14 of aring sector 15.

Within each ring sector 15, the piston vanes 13 and the mating vanes 14delimit two working chambers 16, 17 that can be pressurizedhydraulically, more specifically under the control of the control spool8.

From FIGS. 1 and 3, it can be seen that the clamping screw 9 is centeredrelative to the camshaft 2 by means of a centering collar 119 on thecamshaft 2. The centering collar 119 is supported directly on thecircumference of the clamping screw 9. This centering of the clampingscrew 9 and the camshaft 2 relative to one another in the region of theend adjacent to the camshaft 2 makes it possible to construct the innerelement 110 and the outer element 111 as flat discs. The result is thatthese have ends that lie in planes perpendicular to the axis of thecamshaft 2 and can be covered by likewise flat covers 134, 135 designedas annular covers. In conjunction with the axial clamping of theclamping screw 9 relative to the camshaft 2, the centering collar 119interacting with the circumference of the clamping screw 9 thus allowsdirect alignment of the clamping screw 9 on the camshaft 2, resulting insimplicity of manufacture and easily manageable production of thecamshaft adjuster 1 in terms of fitting clearances. This appliesespecially also to the inner element 110 and the outer element 111 andto the annular covers 134, 135 covering the latter axially, since thesecomponents can all be constructed as flat discs, at least as regards theinteracting surfaces, which allows narrow tolerances in combination withsimplicity of manufacture. This likewise makes it possible, whereappropriate, to clamp the covers 134, 135 against the inner element 110and the outer element 111 without seals, although seals can beincorporated into the interacting surfaces as annular seals without anygreat outlay in such a solution, as indicated at 147. In general,however, such seals are also superfluous because the working pressuresare relatively low and, even without seals, leaks within the scope ofthe fine machining possible with surface grinding are limited to a levelthat can be accepted if the camshaft adjuster 1 is arranged in the chaincase 4.

Pressure medium is fed to the respective working chamber 16 or 17 in amanner not shown specifically via a bearing location of the camshaft 2in the housing of the internal combustion engine and radial holes 20 inthe camshaft 2. From there, an axial passage 21, 22 leads via thecamshaft 2 and the inner element 110 to an annular space 23 in the innerelement 110, this annular space overlapping with radial holes 24 in theclamping screw 9. These holes open into an annular space 25 in thecontrol spool 8. The annular space is situated between annular collars26, 27 on the control spool 8 which delimit the annular space 25axially.

Together with a further annular collar 28 offset in a direction awayfrom the camshaft 2, the annular collar 26 remote from the camshaft 2delimits another annular space 29, which is connected by a radialconnecting hole and an axial hole 30 to the receptacle 31, which opensinto the chain case 4 via a hole 32, the latter passing through thebottom end of the receptacle 31, and a radial connecting passage 33 thatpasses through the centering collar 119 of the camshaft 2.

The ring sectors containing the working chambers 16 and 17 are closedoff axially by the annular covers 134 and 135, which cover areas of theend faces of the inner element 110 and the outer element 111 and areheld against the flat end faces of the inner element 110 and the outerelement 111 by axial clamping screws 38.

To fix the outer element 111 as a vaned rotor in its positioncorresponding to the starting position of the internal combustionengine, this generally 10 corresponding to a retarded position of thecamshaft 2, a locking element 39 in the form of a radial pin is providedin the region of one piston vane 13 of the outer element 111. The radialpin is spring-loaded towards the inner element 110 and has associatedwith it a latching opening 40 in the inner element 110. The latchingopening 40 overlaps with a radial passage 41, which starts from anannular groove 42 provided in the inner circumference of the innerelement 110 and opens into the chamber 16. This annular groove 42overlaps with radial holes 43 in the axial wall of the clamping screw 9.The axial wall forms the guide for the control spool 8 and delimits thereceptacle 31 for the control spool 8. Radial passages 44 (illustratedin broken lines in FIG. 2) are provided in the inner element 110. Theseare offset axially relative to the illustration in FIG. 1 and open intothe other working chamber 17. The radial passages 44 open into annulargrooves 45 that overlap with radial holes 46 in the wall of the clampingscrew 9.

When the internal combustion engine 3 is started, pressure medium issupplied via the radial hole 20 in the camshaft 2 and passes via theaxial passages 21 and 22 into the annular space 25 of the control spool8. In accordance with the starting position, the spool initially assumesa spring-loaded end position adjacent to the camshaft 2 until, with theperformance of the starting operation, the actuator 5 is activated andthe armature 7 is attracted by the actuating magnet, with the resultthat the annular space 25 is moved into overlap with the radial hole 43in the clamping screw 9 and, via the annular groove 42, with the radialpassage 41, and hence supplies the locking element 39 and the chamber 16with pressure medium. The locking element 39 is thereby displacedcounter to the spring force. The locking provided by the locking element39 is cancelled. The outer element 111 is pivoted counter-clockwise (inrelation to the illustration in FIG. 2) in the direction of an advancedposition of the camshaft 2.

Once the desired camshaft position has been reached by appropriatecontrol of the control magnet of the actuator 5, as a function of thecontrol of the engine, the annular collars 26 and 27 of the controlspool 8 are moved into overlap with the holes 43 and 46, thusinterrupting the supply of pressure medium to the chambers 16 and 17 aslong as the camshaft is in its intended position. If displacement occursrelative to this position, owing to leaks for example, the necessaryadjustment is performed by means of the actuating magnet 5, which isadjusted accordingly, operating as a continuous control element, e.g. asa proportional magnet, that is by supplying or releasing pressure mediumto or from one of the chambers 16 and 17.

If the internal combustion engine 3 is switched off, the control spool 8moves back into the initial position. Here, the chamber 16 is connectedto the return by the annular space 29. Thus, the chamber 16 is emptiedand simultaneously allows the pin forming the locking element 39 to bepushed back into its locking position by the spring force. In both endpositions of the control spool 8, the particular chamber that is notpressurized is open to the return.

The configuration indicated provides a camshaft adjuster 1 which is veryshort in the axial direction of the camshaft 2. The inner element 110 isclamped axially against the camshaft 2 and at the same time, centered bythe clamping screw 9, the clamping screw 9, for its part, simultaneouslyforms the centering means for the inner element 110.

While the above detailed description describes the preferred embodimentof the present invention, the invention is susceptible to modification,variation and alteration without deviating from the scope and fairmeaning of the subjoined claims.

What is claimed is:
 1. A camshaft adjuster for internal combustionengines, which is situated in the drive for driving a camshaft by meansof the crankshaft and is to be connected to the camshaft in a centeredand coaxial manner with respect to the latter, comprising: an innerelement which is fixed in terms of rotation relative to the camshaft ispenetrated by a central clamping screw and can be clamped axiallyagainst the camshaft by means of this screw; an outer element which canbe turned relative to the inner element and via which the driveconnection to the crankshaft runs; an accommodation space between theinner element and the outer element for hydraulically pressurizableactuating means for turning the outer element relative to the innerelement; and a control device associated with these actuating means andhaving a multi-way valve integrated into the clamping screw, which, as ahousing, forms an axial receptacle for a centrally situated and axiallydisplaceable control spool, the clamping screw carrying the innerelement engages by its camshaft end in an axial centering collar on thecamshaft and is supported against the latter.
 2. The camshaft adjusteraccording to claim 1, wherein the inner element and the outer elementare designed with flat end faces and are covered over a certain area byannular covers.
 3. The camshaft adjuster according to claim 2, whereinthe annular covers adjoin the centering collar of the camshaft radiallyon the inside.
 4. The camshaft adjuster according to claim 1, whereinthe control spool is connected to the armature of an actuator arrangedfixed relative to the housing and comprising an actuating magnet.